In recent years, there has been a significant amount of commercial interest in the deposition and buildup of metal sheets and plates which are made from a liquid or semiliquid spray impinging on a cooled substrate. Highly attractive combinations of properties and structures are achievable through rapid solidification of a sprayed stream of molten metal. The current deposition techniques include using a high-pressure inert gas jets to break a falling stream of liquid metal into fine droplets, while at the same time imparting a downward acceleration to those droplets. Several technologies presently exist for spray deposition of metals. These include the conventional process known as the Osprey process, the Controlled Spray Deposition process, and the Liquid Dynamic Compaction (LDC) process. These technologies all use a high pressure gas for atomizing a molten metal.
In addition to the above, thermal spraying is also widely used for the applications of coatings which are resistant to oxidation, corrosion, abrasion, erosion, impact and wear. Thermal spray is a generic term for a group of processes used for depositing metallic coatings. These processes, sometimes known as metalizing, include flame spraying, plasma-arc spraying, and electric-arc spraying. The coatings are generally sprayed from a rod or wire stock or from powdered material. The wire or rod is fed into a flame or plasma, where it is melted. The molten stock is then stripped from the wire or rod and atomized by a high velocity stream of compressed gas which propels the material onto a substrate.
A major problem with the convention methods, such as those discussed above, is that they usually use a high pressure compressed gas for atomizing the molten metal. This gas impingement, used as a means for breaking a molten metal stream into fine particles often requires the use of an inert gas, in order to avoid contamination of the molten metal. Inert gases are often expensive, which increases the cost of the process and the resulting product. Due to the fact that the conventional process requires the use of a high pressure or compressed gas for atomizing the molten metal, such process is limited in that use of high-vacuum melting and casting procedures is not possible therewith. Further, when a high-pressure gas, for example, from jets, is used to create a metal spray, some of the inert gas is entrapped in the impinging droplets of the molten metal.